Process for fluxing and brazing parts made of aluminium or aluminium alloy

ABSTRACT

The process is characterized in that one proceeds to prepare a fluxing compound, in that a thin coat of this compound is deposited on at least those of portions of parts requiring to be assembled, then that after partly melting the compound the parts are heated up to brazing temperature.

United States Patent Chartet 1 June6, 1972 [54] PROCESS FOR FLUXING AND[21] Appl.No.: 15,601

2,723,929 1 H1955 Wagner et al 148/26 2,756,497 7/1956 Gale ..29/4952,817,893 12/1957 Cunningham et al. 29/495 X 3,330,028 7/1967 Elbreder..29/495 3,377,183 4/1968 Hurt, Jr. et al 17/21 X 3,573,090 3/1971Peterson ..1 17/17 X F ORElGN PATENTS OR APPLICATIONS 680,344 10/1952Great Britain 148/24 802,483 10/1958 Great Britain ....29/495 236,2134/1966 U.S.S.R. ..29/495 Primary ExaminerJ0hn F. Campbell [30] ForelgnApplication Prion Data Assistant Examiner-Ronald .1. Shore Mar. 5, 1969France ..6906108 Armrneylmirie, y. Snyder and Blm'um Sept, 12, 1969France ..6931230 [57] ABSTRACT [1.3- CI 1 The process is characterizedin that one proceeds to prepare a [51] k 36 fluxing compound, in that athin coat of this compound is [58] Field of Search ..29/495, 496;148/23, 24, 26; deposited on at least those of portions of partsrequiring to be 1 17/105. 1, 105.2 assembled, then that after partlymelting the compound the parts are heated up to brazing temperature. 56R f C'ted I 1 e erences l 6 Claims, 2 Drawing Figures UNITED STATESPATENTS 2,179,258 11/1939 Howarth ..148/26 PROCESS FOR FLUXING ANDBRAZING PARTS MADE OF ALUl'VIINlUM OR ALUMINIUM ALLOY The inventionrelates to the joining by brazing of parts in aluminum or aluminum alloyand principally to the embodying of cooling radiators for motor vehiclesand other similar heat exchangers.

Up till now, for stove brazing parts made of aluminum or aluminumalloys, it has been necessary, first of all, to clean the parts toremove grease, which is generally done by plunging said parts inproducts such as methyl-ethyl-ketone or other grease-removing productsthen into pickling baths of other kinds. This procedure, sometimes,requires rinsing said parts in water before they are dried, then toplunge them into a flux bath made by a dispersion-or solution in water,alcohol, a ketone or chlorinated derivatives-of metallic salts occuringas of chlorides or fluorides of aluminum and alkaline metals or complexsalts of fluoride and derivatives thereof.

At the exit from the flux bath, the parts to be brazed must be stovedand perfectly dried, so that the salts forming the brazing flux coverall the surfaces of the parts to be brazed which are then conveyed to apre-heating cell of the oven, then into a terminal heating cell theparts are heated up to the brazing temperature, this temperatureexceeding 570 C.

In the case of brazing aluminum parts in a flux bath, then metallicsalts and eventually brazing alloys are kept in a melting condition in acrucible and the parts to be brazed are immersed into the melted saltsbath. This second method obviously makes possible to eliminate thepreliminary fluxing operation, and also the stoving operation, but it isstill necessary to clean the parts before dipping them in the bath andgenerally also to preheat them.

In the stoving brazing process mentioned above, it has been ascertainedthat for doing a satisfactory brazing, it was necessary either toutilize relatively considerable'thicknesses of flux on the parts to bebrazed, these thicknesses corresponding to a flux weighing approximately150 g/m2, or else, in order to reduce the flux thickness and hencethecost of the operation, it appeared necessary to first proceed with thestoving operation eliminating the aqueous support of salts in aprolonged manner by means of gas previously dehydrated, then to proceedwith the brazing operation itself in a stoving atmosphere alsodehydrated to a very high degree whose dewpoint is at least about 50 C,which entails very expensive air distributing equipment. y

The invention creates a new fluxing and brazing process by which areeliminated preliminary bath fluxing operations, as well as stovingoperation when furnace brazing is put into practice and through thatprocess the greater part of maintaining and renewing the level of themelted salts baths are eliminated when the bath brazing process isutilized.

Moreover, the quantity vof fluxing salts to be used is very small ascompared with that required up till now, and even less than the smallquantities of salts that are used when a furnace brazing process isutilized with atmospheres having a very slight moisture content whichwere required up till now, and which required an expensive and complexequipment.

According to the invention, a fluxing compound is prepared said fluxcontaining metallic chlorides and fluorides in anhydrous form, and athin even coating of this compound is deposited on at least the portionsof said parts that must be joined together by subjecting this compoundto at least a partial melting for a short time, the brazing of saidparts being done by subsequent heating up to brazing temperatureimmediately after depositing said fluxing compound.

According to an important new feature of the invention, one prepares thefluxing compound from a mixture of metallic salts in an anhydrous state,said mixture is then heated to reach at least a pasty state, the saltmixture then is cooled, crushed and sifted so as to make a finecomposition powder within the size range of about 25 to 150 p. and saidpowder is used for covering the portions of the parts to be brazed bymomentarily melting it, at the moment of deposition, on said parts to bebrazed.

According to an optional feature of the invention, it also becomespossible to braze parts which have not been covered with a brazingalloy, hence which are not very costly, and this while making a highquality braze and enabling perfectly sealtight connections.

According to another optional feature of the invention, an anhydrousfluxing compound reduced to powder is prepared, which is deposited in athin coating on the parts of the pieces that must be assembled together,while submitting this compound to at least partial melting during ashort time, said fluxing compound being pressure sprayed on the parts tobe covered at the same time as the metal particles of a brazing alloy.

Various other characteristics of the invention will moreover be revealedby the detailed description which follows.

Embodiments of the invention are shown, by way of nonrestrictiveexample, in the accompanying drawings.

FIG. 1 is a diagram of an installation for putting the process of theinvention into practice.

FIG. 2 is a diagrammatical section, on a larger scale, of an embodimentof a spray nozzle appearing in the diagram of FIG. 1.

For carrying out the process of the invention covering fluxing andbrazing metal parts of aluminum or aluminum alloy, preferablybut notnecessarily -..covered with brazing alloys, mainly aluminum-siliconalloy containing 2 to 13 percent of silicon, a fluxing compound is firstof all prepared which can be made of components which are normally knownin commerce for preparing aluminum brazing flux in aqueous vehicles, butaccording to the invention, the fluxing compound is constantly kept inthe anhydrous state.

As constituent of a brazing flux for aluminum, it is known to utilizemetal salts, particularly chlorides and fluorides combination, such aslithium chloride, strontium chloride, potassium fluoride, cryolite,sodium chloride, etc..., whose respective quantities can vary withincertain limits, determined by the kind of brazing alloy and also themanner in which brazing itself is carried on, e.g., if brazing takesplace in the stove, or on the contrary, in a bath. For instance, in thepreferred use of the invention for the brazing of parts forming radiatorcores, parts made of aluminum plated on at least one face by analuminum-silicon alloy with a 12 percent silicon content, and whenbrazing is to be done in the stove, a fluxing compound can be used thatconsists of:

-30 parts by weight of lithium chloride -35 parts by weight of sodiumchloride -40 parts by weight of potassium chloride -6 parts by weight ofzinc chloride l 2 parts by weight of cryolite 9 parts by weight ofaluminum fluoride.

The above-mentioned metallic salts respectively have different meltingtemperatures that extend from about 250 to l C.

After mixing said metallic salts, it has been noticed that if thismixture is brought to a melting temperature, it is possible to obtain afluxing compound with a pasty melting limit appreciably extending in a200 to 600 C. bracket.

According to one operation of the process of the invention, theconstituents of the fluxing compound previously mixed carefully in a dryatmosphere receptacle, for instance whose atmosphere has a dew-point ofless than 50 C., are brought to a melting state, then cooled to form asolid mass. This mass is then finely ground, still in a dry atmosphere,then sifted to obtain a powder whose even size composition, lies, forinstance between 25 and 11..

A following operation of the process consists of depositing the preparedanhydrous flux on portions of the parts to be brazed together, and to dothis, the deposition is done at high temperature, i.e., by previouslyheating either the prepared powdered flux, or the portions of the partsto be covered with a uniform coating. The temperature at which thisdeposition is carried out is between 200 and 400 C., and the temperatureselected in the braket depends on the method of deposition chosen, ofwhich some are given hereafter, and of the nature of the parts to bebrazed together, which parts must obviously be free of all dirt,particularly traces of grease, which would risk spoiling the quality ofthe brazing joints.

For depositing the fluxing composition, several methods can beconsidered, according to the invention, and in that which follows,although this is not restrictive from the standpoint of the scope of theinvention, the preferred application is considered to which it generallyapplies, i.e., brazing of radiator cores for motor vehicles.

. In this case, it was found that the best results, with regard tobrazing tubes to secondary heat dissipating elements with which thesetubes are associated, i.e., fins or corrugated intercalaries, likewisethe brazing of the ends ofthe tubes to collectors, were obtained bydepositing a very thin coat of flux on the entire external surface ofsaid core, this coat being as even as possible with regard to itsthickness. By way of example, for subsequently effecting the brazing ofthe tubes to the dissipating elements with which they are provided, theweight of the brazing compound is of about 10 to 40 g/m2, this weightbeing able to be still further reduced in certain circumstances,particularly when the oxide coating has been previously reduced, atleast partially, by a preliminary pickling treatment which isadvantageous to effect, according to the invention, particularly whenbrazing is done in the oven.

'An advantageous method according to the invention for depositing aneven coat of fluxing compound is shown in FIG. 1, in which referencenumeral 1 represents a closed dry atmosphere receptacle containing theprepared flux compound powder, this receptacle being provided with anagitator 2, and being connected, by means of purifying device 3 and aflow regulating unit 4, to a source 5 of compressed air, nitrogen orother gas. The gas brought into the receptacle 1 conveys a regularquantity of powder which is then taken to a dissipating member 6,formed, in the example shown, by a spray n'ozzle fed with combustiblemixtures from cylinders 7 and 8 for instance, containing respectively,the one, oxygen, the other ethylene, propane or another combustibleproduct. This blowpipe,"one embodiment of which is shown in FIG. 2, hasa pipe 9, through which the powder in suspension in the gas coming fromthe source 5 is brought, this powder conveying pipe 9 emerging at theinlet to a blowing burner 10 into which there also emerges an inlet jetof driving gas which can also come from the source 5, and moreover,the'combustible products are conveyed by one or' more channels 12,preferably terminating in an annularoutlet 12a so-that the flameproduced is obligatorily traversed bythe gas and powder carried along bythe gas.

By'this means, the powder is brought to the temperature selected whichdepends on the pan to be covered with the fluxing compound. Said part isdesignated by 13 in FIG. 1, and is placed in the trajectory of the jetcoming from the spray nozzle 6. The part 13 can either be at thesurrounding temperature, or pre-heated, but according to the invention,it has been seen that the best results were obtained when the fluxingcompound is sprayed on, and the part 13 is at ambient temperature orthereabouts, if subsequent brazing is done in the oven.

In addition to the foregoing, it is also advantageous that the spraynozzle 6, as well as the part 13 to be covered, be brought to differentelectrical potentials, for instance by means of electrostatic equipment14, of the kind used in electrostatic paint plants. In this way, one iscertain that all fluxing compound previously melted, at least partially,before reaching said part 13, is evenly distributed on it and thatfluxing compound losses are at a strict minimum.

Another means of depositing the fluxing compound, also advantageous inparticular in the preferred application of the invention to radiatorbrazing, consists of providing a receptacle in which the fluxingcompound powder is kept in suspension in a gas continuously circulating,so that the powder suspension is uniform in said receptacle, and topre-heat the part to be covered to a temperature of 300 to 450 C., sothat the particles of powder in suspension in said receptacle and whichcome into contact with said part melt at least partially upon contactwith the same, while covering it in an even manner.

The heating of the part can be effected before putting it in thereceptacle, or into the receptacle itself, which can be done in variousways known in the technique, for example by submitting the part to aninfra-red ray, or passing an electric current into it of sufficientintensity for bringing the temperature to the level stated above, orelse by subjecting it to the action of high frequency current, etc.

When the powder is sprayed that has been brought to a melting pointbefore reaching the part to be covered, obviously other appliances canbe used than that of FIG. 1 and 2, and it is possible to suppress anyflame by bringing a driving gas preheated to a sufficient temperaturefor partially melting the powder, or else, it is possible to use aplasma spray-gun or centrifugal cupels associated, or not, with heatingmembers by radiation, conduction or the like. 7

When brazing is done in the oven, which is the preferred working methodaccording to the invention, then the depositing of the fluxing compoundon parts to be brazed, in this case a radiator core, is done immediatelybefore introducing said cores into the oven, so that the depositedfluxing compound has not had time to hydrate, which enables an oven tobe used in which it is not necessary to carry out a considerablepreliminary dehydration of the air or other gas in it, as has beennecessary up till now.

In the case of brazing radiator cores in an oven and operating theinvention, it has been noticed that particularly satisfactory resultswere obtained by using extremely small quantities of fluxing compoundsand taking care to proceed as follows:

After assembling, the core is subjected to cleaning, pickling, rinsingoperations, by successively putting it into a de-greasing bath and oneor more acid or alkaline pickling baths, then into a rinsing bath heatedto about C. I

Actually, it has been noticed that the core was brought in a few secondsto ambient temperature, owing to its low heat inertia and that it driedspontaneously owing to the rapid evaporating of the hot rinsingsolution. Seeing that also the core is at the ambient temperature in avery short'time, the oxide coat, whose greater part is destroyed in saidpickling bath, has not time to reform if the precaution is taken ofsubjecting said core to the fluxing compound deposit just after drying,this fluxing compound then forming a coat protecting the core during itspreheating in the oven to which it is taken for brazing. The depositionaccording to the process described in the foregoing of the fluxingcompound also has a considerable interest when the brazing of parts, inparticular, radiator cores, must be clone by plunging these parts into amelted salts bath according to the process currently used in thetechnique. Actually, seeing that the part to be brazed carries thenecessary quantity of fluxing compound for proper brazing, then eachpart plunged into the brazing bath brings to the bath the necessaryquantity of fluxing compound for effecting brazing. Consequently, thecompounds contained in the bath are renewed by adding the fluxingcompound brought by each part, and also, the quantity of fluxingcompounds necessarily removed by each part after brazing, when withdrawnfrom the bath, is obviously also compensated by the quantity of fluxingcompound brought by this part. Thus the bath remains at a steady level,eliminating the necessity of proceeding, as done up till now, toperiodical new additions of fluxing compounds to the bath, these newcontributions being delicate operations on account of the bathtemperature and the precision of the composition of the products that itmust always contain.

Also, this process has the advantage of bringing the parts to be brazedwhile having maintained the advantages of pickling, consisting ofpartially, or totally eliminating the oxide coating, up to the brazingoperation itself, thus enabling a less agressive flux to be used, whichis consequently, generally cheaper.

When the parts to be brazed are not covered with a brazing alloy, apowdered anhydrous flux is prepared as described in the foregoing, andparallely, an aluminum-silicon alloy owder is prepared, the alloycontaining 2 to 13 percent of silicon, this aluminum alloy powder beingsifted so that its size composition is approximately 150 n.

The next operation of the process consists of mixing the aluminum powderwith the powder of flux, the proportion of the mixture being about 2 to5 parts by weight of flux powder for one part by weight of the metallicpowder. The powder mixture thus prepared is used for supplying, asdescribed in the foregoing, a spray-gun by which said powder is sprayedon the parts to be brazed.

When the spray-gun is at work, the brazing alloy is protected by thevaporizing of the finest particles of flux, and the brazing metal ismade very adherent to parts on which it is sprayed, because this metalis sprayed at the same time as the flux in a liquid or pasty state, andsince the impact force to which said metal is subjected strikes theportion of the parts to be covered. 1

Moreover, seeing that the brazing alloy has a much higher density thanthe flux in the liquid state with which it is sprayed, it has beennoticed that the brazing alloy flows to the bottom part of the coatcovering the parts, i.e., that it is covered by a coat of flux thusacting as a protecting coating as long as brazing itself has not beendone.

To do brazing, the covered parts are placed in an oven where they areheated up to the brazing temperature according to the kind of brazingalloy, for instance often in the vicinity of 600 C.

In an alternative of the process described above, the brazing alloy isnot reduced to powder but formed by a wire for supplying a spray-gunsimilar to that used in metallurgy, this spray gun then being furthersupplied with flux powder conveyed by an air jet or other compressedgases, so the particles of melted alloys and flux, also melted, aredischarged at a sufficiently high speed so that they properly adhere tothe part to be covered.

I claim:

1. A process for fluxing and brazing parts made of aluminum and aluminumalloys with a brazing alloy for assembling portions at least of thesame, comprising the steps of:

preparing a brazing flux in an anhydrous form; powdering said anhydrousflux; hot spraying said powdered flux on said portions of parts to bebrazed, said spraying being conducted at a temperature substantiallyequal to the melting temperature of said flux, whereby said flux isadhered to said portions of parts kept at ambient temperature; and

heating said parts to brazing temperature in the presence of saidbrazing alloy;

whereby the flux deposited is initially melted, and said brazing alloyis subsequently melted to braze said parts along said portions wetted bysaid melted flux.

2. A process as set forth in claim 1 wherein said flux is heated between200 and 400 C by blowing compressed air with the powder of flux, thenpassing said powder contained in the compressed air through a flame of aburner, whereby flux is heated only during a very short time.

3. A process as set forth in claim 1, wherein said parts covered withhot sprayed flux is preheated toward the brazing temperature, thenbathed in a melted flux bath heated at the brazing temperature, wherebysaid sprayed flux prevents oxidation during preheating and compensatesloss of flux of said melted flux bath having a flux composition of lightreactivity.

4. A process as set forth in claim 1, wherein said parts to be brazedare firstly submitted to pickling, to rinsing in hot water, to drying atambient temperature, then to hot spraying fluxing immediately whendried, whereby said sprayed flux forms a protective layer preventingoxidation.

5. A process as set forth in claim 1 wherein said brazing alloy ispowdered, then sprayed simultaneously with said flux at the sametemperature as said flux, whereby said powdered alloy is renderedadherent to said part with said flux without being melted.

6. A process as set forth in claim 5, wherein said brazing

2. A process as set forth in claim 1 wherein said flux is heated between200* and 400* C by blowing compressed air with the powder of flux, thenpassing said powder contained in the compressed air through a flame of aburner, whereby flux is heated only during a very short time.
 3. Aprocess as set forth in claim 1, wherein said parts covered with hotsprayed flux is preheated toward the brazing temperature, then bathed ina melted flux bath heated at the brazing temperature, whereby saidsprayed flux prevents oxidation during preheating and compensates lossof flux of said melted flux bath having a flux composition of lightreactivity.
 4. A process as set forth in claim 1, wherein said parts tobe brazed are firstly submitted to pickling, to rinsing in hot water, todrying at ambient temperature, then to hot spraying fluxing immediatelywhen dried, whereby said sprayed flux forms a protective layerpreventing oxidation.
 5. A process as set forth in claim 1 wherein saidbrazing alloy is powdered, then sprayed simultaneously with said flux atthe same temperature as said flux, whereby said powdered alloy isrendered adherent to said part with said flux without being melted.
 6. Aprocess as set forth in claim 5, wherein said brazing alloy is reducedto fine powder of particle size about 150 Mu , and is mixed with thefluxing compound itself reduced to powder of size between 25 and 150 Mu, the proportion of brazing alloy being one part by weight for 2 to 5parts by weight of fluxing compound.